The Occupational Safety and Health Administration, complying with a court-ordered deadline, yesterday proposed a more restrictive standard for worker exposure to ethylene oxide, a chemical widely used to sterilize hospital equipment.

The proposal marks the first time since the Reagan administration took office that OSHA has moved to tighten restrictions on chemical health hazards in the work place. It met with mixed reviews from the unions and the health group that had sued for the new controls.

An estimated 140,000 U.S. workers, most of them in hospitals or the health care industry, are exposed to the gas. Ethylene oxide has been implicated in an increased incidence of leukemia and spontaneous abortions among Scandinavian health care workers. Government toxicologists are currently conducting at least three additional studies on possible links between the gas and chromosomal damage.

"The proposed standard , according to our risk assessment, will greatly reduce the mutagenic, reproductive and carcinogenic effects associated with" ethylene oxide, OSHA administrator Thorne G. Auchter said in a statement. The current level, he said, "does not provide adequate protection for these workers."

The standard proposed yesterday would lower permissible daily exposure limits in the work place to one part of the chemical per million parts of air, averaged over an eight-hour day. The current standard, adopted in 1971, set a 50 parts-per-million limit.

The new standard does not propose an upper limit for one-time exposure, however.

Pointing to that, one union health specialist called the proposed regulation "poorly thought-out . . . a kind of a joke of a standard." The official, Linda Lampkin of the American Federation of State, County and Municipal Employes, said, "More and more toxic effects are being shown from one-time exposures."

One government official familiar with the standard said that the Environmental Protection Agency, which regulates ethylene oxide's use as a pesticide, suggested two weeks ago that OSHA include a ceiling limit in its proposal. Agency officials have disagreed over where EPA's jurisdiction over the chemical ended and OSHA's began.

Sidney Wolfe, director of the Health Research Group, which had sued to force OHSA to promulgate an emergency standard, pointed out that an emergency standard would have offered the new protections before the time-consuming rule-making process is completed.

Wolfe's group succeeded earlier this year in getting a federal district judge to order OSHA to propose an emergency standard, but that order was nullified by the U.S. Court of Appeals for the District of Columbia. Instead, the appeals court gave the agency 30 days to propose a tighter standard. That deadline expired yesterday.

A public hearing on OSHA's proposal is scheduled July 19.